Coverting Hd mkv Software

hello all, I would need advice on software for conversion of film which is in HD 720p or 1080p!
I have been the acquisition of a multimedia player Western Digital TV box that reads the format well, HD h.264 MKV x264 ....
my problem is that I have just the film in HD and going very well or else I have the picture but no sound after multiple adjustment! I have also read the reports and it is true that some audio files are not taken into account! the only solution I've found it is to take my movies and convert them all by keeping the HD quality but with a codec compatible sound! So I work at the moment with Xilisoft HD video converter. I was wondering if you can advise me another software for it? because that is what I keep with Xilisoft as a good format of 720p or 1080p and is it normal that my finished file to MP4 so instead of MKV that I find is not passing?

thank you to all of you!

Before doing so, I advice you to update the firmware (1.01.01) if this is not done.

http://www.wdc.com/en/products/wdtv/

Maybe this will settle the problem of decompression of the audio.

thank you but I've already updated my firmware to 1.01.02!

The only issue with encoding with x264 is that it take a very long time to complete a high quality encode even on the most modern machine. It's a very good codec for encoding HD captures to managable sizes but just isn't practical for use on a recurring and/or automatic basis.

The other downside is that you need a fairly modem machine to smoothly playback high-quality x264 encodes, especially high bitrate 1080p. I use CoreAVC for my decoder and the best solution I've found for playback on my C2D machine.

I still prefer sticking to the source MPEG2 transport streams as I'm able to use the NVidia Purevideo decoder with little CPU overhead. I'm still having minor issues with dropping frames with 1080i material which baffles me as CPU is usage 20% and the video card is a 7950GT with the latest Forceware and Purevideo installation.

Goto doom9.org, the best site for video encoding on the internet, just maybe not extremely beginner friendly, but then if you have EVO files, I assume you are not that inexperienced a user

BTW, I hope you know that such a conversion will take a while, even on a modern dual-core PC.